Mechanical overspeed trip for rotating machinery



Oct. 24, 1967 J. w. SCHLIRF 3,348,420

MECHANICAL OVERSPEED TRIP FOR ROTATING MACHINERY Filed Sept. 7, 1965 INVENTOR. JOHN w. SICHLIRF.

BY M

ATTORNEY.

United States Patent 3,348,420 MECHANICAL OVERSPEED TRIP FOR ROTATING MACHINERY John W. Schlirf, Jeannette, Pa., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Sept. 7, 1965, Ser. No. 485,310 2 Claims. (Cl. 73-538) ABSTRACT OF THE DISCLGSURE An overspeed trip assembly for use in a rotary shaft cavity employing a trip button mounted on a Belleville spring, centrifugal force acting on the trip button causing the spring to move beyond its snap-over point to project the button beyond the surface of the shaft to contact a suitable shutdown switch.

This invention relates broadly to apparatus for automatically limiting the maximum speed of rotating shafts, more particularly to limiting the maximum speed of extremely high speed shafts. Still more particularly, this invention relates to a shaft of speed limiting device employing a Belleville spring as the trip switch operating device.

Ordinary speed limiting devices, when employed on extremely high speed shafts, are subject to excessive friction which causes unavoidable inaccuracies. To combat the friction problem, improved speed limiting devices were developed using Belleville springs. However, these Belleville spring devices employ a rather sophisticated mechanism comprising many parts, linkages, and so forth, and are subject to the inaccuracies and expense resulting from such construction.

It is therefore an object of this invention to provide a simplified Belleville speed limiting device providing for more economical construction and assembly.

Another object of this invention is to provide a Belleville trip speed limiting device acting directly on the trip speed valve or switch to eliminate inaccurate and costly linkages.

It is a further object of this invention to provide a small, compact Belleville trip speed limiting device for use in small rotary machines which cannot accommodate the present, rather large and complicated Belleville speed limiting devices.

This invention relates to a Belleville spring, shaft speed limiting device and comprises a Belleville spring mounted concave side up in a radial cavity in the shaft of a rotary machine, the spring being held in place by a suitable retainer, a trip button mounted in the center hole of the spring and a trip-switch plunger mounted in close proximity to the shaft so as to move radially of the shaft when contacted by the trip button. The aforesaid elements a're so proportioned and arranged that when centrifugal force acting on the Belleville spring and the trip button reaches a certain predetermined limit, the Belleville spring will snap-over, causing the trip buttonn to project beyond the surface of the shaft and strike the trip switch plunger which in turn will cut off power to the driving machine.

The invention will be further described with reference to the accompanying drawing forming a part of this specification and showing by way of illustration, one preferred embodiment wherein:

The figure is a vertical fragmentary sectional view of a rotary machine shaft containing the Belleville trip device which is the subject of this invention.

Referring to the attached drawing, there is shown a rotary machine shaft 1 having a stepped radial cavity therein comprised of a large diameter shallow section 2 and a smaller diameter but deeper section 3 coaxial with the first section 2. The cavity contains a shoulder 4 defined between sections 2 and 3.

Disposed within the cavity and supported by shoulder 4 is a trip assembly 5, comprised of a conical shaped Belleville spring 6, a trip button 8 mounted in the center hole of spring 6, having a round head 9 connected to a threaded shaft 10. The trip button 8 is retained in the spring 6 by a lock nut 11 threaded onto shaft 10.

Trip assembly 5 is held in the cavity of the shaft by a suitable retainer 13 having a central aperture 14.

A trip switch plunger 12 is mounted radially of the shaft 1 on the centerline of the cavity sections 2 and 3 in close proximity to the shaft 1. It will be understood that the trip switch plunger 12 is connected to any convenient device capable of interrupting the power flow to a driven machine and thereby shut down the machine.

The trip assembly 5 is so situated in the shaft cavity that when shaft 1 exceeds the desired number of revolutions per minute, centrifugal force acting on the confined trip assembly will cause the spring 6 to snap over, thereby projecting trip button 8 through retainer aperture 14 above the surface of shaft 1 where it will contact plunger 12 which in turn will cut off power to the driving machine.

While I have described a preferred embodiment of the invention, it will be understood the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

I claim:

1. In combination with a rotary shaft having a cavity therein, a shaft overspeed trip assembly comprising a Belleville spring, a trip button extending through the center hole of the Belleville spring, and means for releasably securing said spring to said trip button; said trip assembly being disposed within said cavity, a retainer for maintaining said trip assembly within said cavity, said assembly being operable to project the trip button beyond the limits of the cavity in response to centrifugal forces generated by rotation of said shaft, said forces being sufiicient to stress the Belleville spring beyond its overcenter position.

2. In combination with a shaft having a cavity therein, said shaft cavity having a shallow cylindrical first section disposed radially of the shaft axis, said first section having threads formed on its cylindrical side wall, said shaft cavity having a second cylindrical section coaxial with said first section, said second section having a smaller cylindrical diameter and a greater depth than said first section so as to form a shoulder between the cylindrical walls of said sections, an overspeed trip mechanism comprising a Belleville spring, said spring being of smaller diameter than the said first cavity section and of greater diameter than the said second cavity section, a trip button mounted on said spring, said trip button having a head portion and a shank portion, a lock nut threaded on said shank portion, said button shank having a shaft diameter slightly smaller than the diameter ofthe center hole of said spring so that the said button shaft fits through said spring center hole, said trip button head and said nut being of greater diameter than the said spring hole, said trip button being mounted on said spring with the head of said button projecting above the upper surface of said spring, the button shaft being disposed in the axial hole of said spring and the lock nut on said button being disposed on the underside of said spring, a disk-like retainer for holding said trip assembly in said cavity, said retainer having threads formed on its exterior cylindrical wall for engagement with the threads on the Wall of the first cavity section, said retainer hav- 4 ing an axial hole disposed therein, said assembly being operable to project the trip button head beyond the limits of the cavity in response to centrifugal forces generated by rotation of said shaft, said forces being sufficient to stress the Belleville spring beyond its overcenter position.

References Cited UNITED STATES PATENTS 2,027,848 1/1936 Warner 743 2,598,157 5/1952 Everett 10279 2,860,865 11/1958 Gardner 73538 MILTON KAUFMAN, Primary Examiner. 

1. IN COMBINATION WITH A ROTARY SHAFT HAVING A CAVITY THEREIN, A SHAFT OVERSPEED TRIP ASSEMBLY COMPRISING A BELLEVILLE SPRING, A TRIP BUTTON EXTENDING THROUGH THE CENTER HOLE OF THE BELLEVILLE SPRING, AND MEANS FOR RELEASABLY SECURING SAID SPRING TO SAID TRIP BUTTON; SAID TRIP ASSEMBLY BEING DISPOSED WITHIN SAID CAVITY, A RETAINER FOR MAINTAINING SAID TRIP ASSEMBLY WITHIN SAID CAVITY, SAID ASSEMBLY BLY BEING OPERABLE TO PROJECT THE TRIP BUTTON BEYOND THE LIMITS OF THE CAVITY IN RESPONSE TO CENTRIFUGAL FORCES GENERATED BY ROTATION OF SAID SHAFT, SAID FORCES BEING SUFFICIENT TO STRESS THE BELLEVILLE SPRING BEYOND ITS OVERCENTER POSITION. 